"Increasingly desperate" Scottish nationalists will pull any trick they can when Holyrood returns to business for its unprecedented summer session after the Commonwealth Games, according to Better Together leader Alistair Darling.
The SNP voted to change Holyrood's recess dates to sit in August before the referendum "purdah" period begins, giving the Scottish Government the opportunity to announce new policies and initiatives ahead of the period of silence.
About a quarter of Scots have registered for a postal vote - rising to a third in some areas - meaning they will be casting their votes from the end of August, Mr Darling said.
"That means that we have a short, critical time but we are increasingly confident about the arguments that we are making," he said at the opening of a Better Together campaign office in Paisley, Renfrewshire.
"As our confidence increases, it's manifestly obvious that the nationalists are running out of arguments and running out of time, which is why I suspect that after the Commonwealth Games you will see them become increasingly desperate in the things that they say."
He added: "We are obviously anticipating that the nationalists, in their desperation, will be desperate to pull any trick they can when the Scottish Parliament is sitting or when it is not."
The Scottish Parliament returns to business on August 5, two days after the Commonwealth Games' closing ceremony.
Mr Darling said Scots can be just as proud of Team Scotland's early successes in the Games as they were of Team GB in London 2012.
He added: "Scotland's medal haul just on day one is a demonstration of just how many excellent sportsmen and women we have in Scotland, and I hope we win many more medals.
"What it demonstrates is that each of the countries of the UK can do an awful lot on their own, but they can also do an awful lot being part of the UK."
The former chancellor also welcomed the news that Britain's economy is growing faster than any other developed country and the Royal Bank of Scotland's largest profit announcement since he bailed them out in 2008.
But he said the present Tory-led UK Government's policies have held back the recovery.
He said: "What we are seeing today is that there is a recovery.
"It is running far more slowly than I anticipated because I think the Conservatives' approach in 2010 was profoundly mistaken and held back that recovery.
"What I would say, and many commentators are saying this, is that while the recovery is welcome, it is by no means established.
"This is a very bumpy road but I always said when I was chancellor, when we set out our recovery programme from 2009 onwards, that it would come but it would take a long time to come.
"I am just sorry that because of what the present Government has done that it is running later than it otherwise would have been. They predicted recovery two years ago."
Scottish Deputy First Minister Nicola Sturgeon and the Local Government Minister Derek McKay opened a Yes Scotland shop in Paisley on Monday.
Ms Sturgeon said: "For Labour voters seeking a fairer and more equal country, a Yes vote offers the only real opportunity of making that a reality.
"It may be an irony, but it is precisely because Labour voters in Scotland have not traditionally been motivated by constitutional politics that increasing numbers are making up their mind to vote Yes.
"Defending a Westminster establishment that works for the few - and shows a contempt for the needs of the many - is the constitutional politics of the No campaign.
"'Westminster knows best' is the very essence of the No camp's message but it is demonstrably untrue, and it has a rapidly diminishing appeal among Labour voters in Scotland who want a political system capable of delivering progressive change, not propping up vested interests.
"That's why the polls show more Labour supporters moving to Yes. People are seeing the excitement and possibility of independence to ensure that the huge wealth of Scotland works for everyone. We are a nation of five million, and we cannot afford to leave anyone behind. An independent Scotland will want - and need - the talents and energy of all the people, which is the guarantee of a fairer sharing of wealth.
"A Yes vote is the chance of a lifetime for Labour voters to reclaim their politics and their party - and put Scotland on a path towards the goals and ambitions they support.
"Instead of seeing up to 100,000 more children pushed into poverty because of Westminster austerity, we can get rid of Trident nuclear weapons and transform childcare to benefit 240,000 children. I have canvassed many Labour voters in many elections, and failed to persuade many of them to vote SNP.
"But I have yet to meet a Labour voter yet who puts bombs before bairns, which is one reason why I have spoken to so many in this referendum campaign who are voting Yes."